A drone and a passenger plane came within metres of crashing into each other near the Houses of Parliament, a report says.

The "silver drone with a balloon-like centre and four small rotors on each corner" was spotted by the pilot of the Embraer 170 at 2,000ft on 13 September, according to the UK Airprox Board.

The pilot assessed the risk of collision as "high" and claimed it was pure chance they did not hit each other, the board's report said.

The jet had been passing in the vicinity of the Houses of Parliament at more than 184mph as it came in to land at London City Airport.

The pilot estimated that the drone came within 20 metres (65ft) of the plane, which can carry up to 76 passengers, passing down the left hand side of the aircraft.

The incident was classed as category A by the board - the most serious, where there is a high chance of collision - because the drone operator posed a "flight safety risk" and was flying the craft without permission.

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The report also documents five other incidents involving drones between August and September last year.

Three involved passenger jets either coming in to land or flying out of major UK airports, including Manchester, Stansted and Heathrow.

One pilot flying a Boeing 777 jet on 22 September at 2,000ft said the drone "just missed the tip of the starboard wing".

Another, piloting a Boeing 737 flying out of Stansted on 13 September, said a drone passed just three to four metres above the jet.

None of the drone operators, including the one involved in the incident in central London, could be traced.

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The current rules on drones state that they must not be flown in any way that could endanger people or property.

It is illegal for the unmanned aircraft to be flown over streets, towns and cities.

The rules also say they must be kept well clear of airports and airfields.

A UK Civil Aviation Authority spokesman said drone operators must act responsibly, observing all of the relevant rules and regulations.

He said: "Drone users have to understand that when taking to the skies they are potentially flying close to one of the busiest areas of airspace in the world - a complex system that brings together all manner of aircraft including passenger aeroplanes, military jets, helicopters, gliders and light aircraft"